The invention relates to a method of manufacturing a semiconductor single crystal of a III-V compound which consists essentially of a first element which is comparatively volatile as compared with a second element. This method comprises a first step in which a quantity of a semiconductor III-V compound in polycrystalline form is heated to its molten form by raising the temperature of a first heating zone of a furnace, the said quantity of the III-V compound being placed in a boat in a closed space in which a given pressure of the first element is maintained by means of a quantity of the comparatively volatile element which initially is placed at a given point of the said space, at lower temperature, opposite to a second heating zone, followed by a second step in which the melting bath of the stoichiometric mixture is caused to crystallize progressively, by moving the said boat relative to the temperature profile of the said first zone towards less high temperatures.
A method of this type is one of the most frequently used for the preparation of single crystals of gallium arsenide. It is known as "horizontal Bridgman" process. In the process the crystallization of the semiconductor compound is determined by a slow horizontal displacement of the furnace in which the desired temperature profile is maintained between the heating zones is maintained. There is also a modified embodiment of this method, also known as "gradient freeze", in which the boat and furnace assuming a fixed position relative to each other, the crystallisation is obtained by a progressive modification of the temperature profile of the furnace.
These methods are well known in the semiconductor industry and a description thereof is to be found, for example, in the article of A. R. Von Neida en J. W. Nielsen, entitled "Synthesis and Crystal growth of GaAs and GaP for Substrates" published in Solid State Technology, April 1974, pp. 90 and 91. In the same article there is also described a method of synthesising GaAs which, while using substantially the same apparatus, is distinguished by the fact that the starting materials consist of separate elements of the compound, namely gallium and arsenic. These are introduced respectively, on the one hand in the boat and on the other hand at the point of lower temperature of the space. The synthesis is then carried out by reaction of arsenic vapour and gallium which is brought to a temperature which is slightly higher than the melting point of GaAs. The crystallisation phase of the compound then progresses in the same manner as in the first-mentioned method, that is to say the crystallisation method starting from a batch of molten polycrystalline material.
As regards the efficiency of this method, there should be distinguished between the yield in weight of obtained raw material and the yield in weight of single crystal which can be used for the manufacture of the devices. The yield in weight of raw material is very high in all cases and is near 100%. The yield of the resultant single crystal on the contrary varies according to various factors, in particular: the quality of the apparatus used, the methods used and certain undetermined causes, so that in general this yield is significantly lower than unity.
In the case in which there is synthesis of the compound succeeded by crystallisation in the absence of a monocrystalline seed, the possibilities of obtaining a single crystal are comparatively small.